Suggest Treatment For Severe Stomach Cramps Despite Having A Colonoscopy

My husband had his colonoscopy in July...all was well, but not completely cleaned out so another one in 3 years. He experienced gas pains, but not just the usual so Dr ordered an x-ray. All well. His stomach cramps so badly that he will lie on the sofa for hours...diahrrea, gas, etc. Called dr back and he checked thryroid-normal, so prescribed med for irritable bowel. He has begun to loose weight. Could you guide us in some sort of what to do next procedure? He had also gone on a 50 mile hike on Appalachian trail in June..used water purifier, but I am also worried about bacteria. Thanks.